The present invention is associated generally with the field of acoustic cardiography, and more specifically relates to controlling heartbeat-assisted, pacemaker (implanted or external) pacing in relation to a pacemaker-equipped subject's level of heart-rate activity. Those skilled in the art will recognize that this field of acoustic cardiography involves the cooperative, information-integration use of both heart sounds and ECG information processed in different ways to obtain, selectively, various important heart-functionality parameters which correlate to, and help one to understand, the hemodynamic (pumping and filling) behavior(s) of a subject's heart. Such integration characterizes and underpins important aspects of the present invention.
While it will be very evident to those skilled in the art that the methodology of the present invention may be employed successfully in a number of different heart-pacing manners of operation, a preferred and best-mode approach toward practicing the invention is disclosed herein, for illustration purposes, specifically in the context of biventricular, pacemaker pacing.
State of the art thinking with respect, generally, to the employment and control of pacemaker therapy for a subject who is equipped either with an implanted or an external pacemaker, effectively involves adjusting aspects of the subject's pacing rate in accordance with heart-functionality physiologic demand. Various approaches have been proposed to accomplish this goal. In this context, it is important that any such therapy be applied in a manner which is capable of supporting best-possible heart-functionality behavior in relation to subject activity level and metabolic demand during the different periods in a day.
For example, at nighttime, when the human body reduces its metabolic demand, the intrinsic heart rate of a subject is typically lower in accordance with operation of the subject's neurohumoral control mechanism. This reduced-cycle-rate, nighttime condition is referred to in the medical arts as involving reduced sympathetic tone. During such a time of low (i.e., lower than “normal”) subject activity, a time which we refer to herein generally as being a rest-phase time, heart-failure patients, especially at very low activity times, can experience a high fluid load in the heart—a load which the heart muscle normally cannot handle adequately, particularly in a circumstance where the subject is lying down. As a consequence, such patients can go into a decompensated state which leads to fluid being pushed back into the lungs, accompanied by symptoms of shortness of breath which need to be treated just as soon as possible.
In this context, it is typically and conventionally assumed, in accordance with prior-art practice, that a predetermined reduction in a pacemaker's pacing rate will be adequate to deal with such a potential decompensation condition. And, with respect to most of today's currently available pacemakers, medical personnel can preprogram different predetermined pacing rates to apply at different activity-level periods during the day, with heart activity level being generally detectable by means of various conventional mechanical and/or physiologic sensors that are either disposed within, or otherwise operatively associated with, a subject's pacemaker.
The present invention recognizes, generally, that an approach involving increasing a subject's heart-pacing rate during a low (lower than normal)-activity-level rest phase, and especially when the subject is lying down at any time, can potentially prevent the mentioned decompensation. The invention also recognizes, specially and uniquely, that pacing rates employable to deal with decompensation should not be rigidly preprogrammed, as is the case with prior-art, decompensation-minimizing approaches.
Accordingly, key features of the present invention specifically address this just generally outlined rest-phase condition as it relates to the subject's heart functionality, particularly with a focus toward minimizing the mentioned fluid buildup problem, and doing so in a manner which is based upon carefully monitoring (a) a subject's level of heart-rate activity, and (b) one or several identified heart-functionality parameters, and then relatedly adjusting and controlling a pacemaker's (a) pacing rate, (b) pacing intensity, (c) atrio-ventricular (AV) delay and/or (d) inter-ventricular (IV) delay, behavior(s). It should be understood that the “rest-phase” concept expressed herein is treated in the practice of the present invention as a concept which preferably relatively broadly encompasses a wide range of lower-than-“normal” (or high) heart rate levels.
More specifically, and as will be seen, implementation of the present invention focuses, in the related context of feedback-adjusted, rest-phase (not necessarily at night, or while lying down), heart-therapy pacing, on the development and defining (computer calculation) of what is referred to herein as an acoustic cardiographic therapy, or control, (AC) value (also referred to simply as an AC Value). This AC Value “entity”, utilizing computer processing, is determined from (i.e., is based upon) one or more heart-functionality parameter(s) that are especially relevant to the heart pumping and filling functions particularly as they are associated with a subject's activity level. It is computed on the basis of key, input, physiologic information, such as heart-sound and ECG information. In this setting, the invention specifically recognizes the special utility, in different circumstances, of several, important heart-functionality parameters as bases for calculating, and then employing, AC Values that are deemed to be the most useful for controlling the rest-phase pacing operation of a pacemaker. These parameters are three in number. They include S3, EMAT and % LVST.
In certain circumstances, the S3 parameter may be used as an averaged singularity for AC-Value calculation purposes. In certain other circumstances, an appropriate averaged and computed mathematical combination of two or all the three parameters may be the best to use. Non-exclusive illustrations of averaging and mathematical combining of heart-functionality parameter values involved in the calculation of AC values are given below.